The immune and neuroendocrine system interact through communication mediated on a molecular basis by the production of similar ligands and receptors. Specifically, the immune system both produces and responds to thyrotropin (TSH). We have postulated that there exists a hypothalamic- lymphoic-thyroid (HLT) axis. We have identified and partially developed and characterized an in vitro T cell model (Molt 4 lymphoblast) which expresses thyrotropin in response to stimulus with thyrotropin releasing hormone (TRH). In addition, these cells also express cell surface binding sites for TRH., The overall goal of this proposal is to biochemically and molecularly characterize the TSH and TRH receptor(s) produced by the Molt 4 T cells. This information will answer whether the Molt 4 cell model is an accurate model of pituitary TSH production by thyrotroph cells. The experiments will include determination of bioactivity of the Molt 4 cell derived TSH on cells of the neuroendocrine system as well as on cells of the immune system. The ir-TSH will be analyzed at the level of RNA to determine whether the genes for TSH and beta are expressed in the same kinetic fashion, and use the same number and types of TSH mRNAs as the putuitary. The reulation of TSH protein and mRNA will be analyzed in response to primary and secondary regulators of pituitary derived TSH. In addition, cytotines from the classical immune system will be assayed for their ability to regulate the ir-TSH. The results may provide in vitro relevance to the role of if-TSH production in vivo in the mileau of an immune response. These type of experiments will determine whether the genes are expressed and regulated using similar pathways as those used by the pituitary system. These data will define whether the Molt 4 cell model is a representative model for studying mechanisms of regulation of the HLT axis that may be similar to the mechanisms of regulation of the HPT axis. Additionally, the data will lend information to pathways of regulation that may be unique to the immune system. The Molt 4 cells appear to have two binding sites for TRH, a low affinity site similar to the pituitary TRH receptor and a high affinity site that is unique to the immune system. This project proposes to characterize these binding sites, biochemically and with regards to second messenger pathways. The results of these experiments will be compared to the TRH receptors on GH3 rat pituitary cells. The binding chain(s) of the TRH receptor(s) will be determined, purified and used for production of a monoclonal antibody. The antibody will be used as a reagent to screen a lambda gt11 cDNA library. Finally, we propose to clone the cDNA to the binding chain of the TRH receptor(s) on the Molt 4 cells. The development and characterization of the Molt 4 cell in vitro model and verification of its usefulness as a system for studying the genes for TSK and TRH receptors is important from a basic and clinical science standpoint. There is currently no stable in vitro cell line that serves as a complete model for TSH production and is therefore a model for the HPT or HLT axis. Therefore, this model may prove very useful for analysis and characterization of the structure and regulation of the genes and promoters for human TSH alpha and beta. In addition, mechanisms of regulation of the HLTT and HPT axis may be addressed using this model. The purification, development of a monoclonal antibody and cloning of the TRH receptor(s) will be the first time that a receptor for a neuroendocrine releasing hormone expressed on the immune system has been cloned. These analyses will be useful in the development of reagents for probing the HPT and HLT axis. from a clinical science standpoint, these reagents may serve as probes in studying individuals with defects in the HPT and/or HLT axis.